1. Field of the Invention
This invention relates to a tappet structure improved to have a friction-resistant property, and particularly concerns to a tappet structure well-suited to an internal combustion engine of OHV (Over Head Valve) type.
2. Description of Prior Art
In order to cope with high rpm and high output of an engine, OHC (Over Head Camshaft) type of an internal combustion engine has been increasingly introduced in which a rotary movement of a cam directly allows to move a rocker arm so as to operate a valve.
However, OHV type of an internal combustion engine has been employed in a field of industrial engines and large-scale diesel engines.
In the OHV type of an internal combustion engine, a cam allows to axially move a tappet body which causes to move a rocker arm by way of a push rod, thus causes to operate a valve so as to alternately open and close an intake and exhaust port each communicated with a combustion chamber.
In this case, wear appeared between the tappet body and the cam can't be ignored when taking a demand of high output of the engine into consideration.
On the other hand, light-weight valve system is required to reduce friction loss. In accompany with the request, it is necessary to make the tappet body light-weight. For this reason, it has suggested that whole of the tappet body itself would be integrally made of ceramic material. This tappet, however, makes the material expensive, and rendering it difficult to machine, thus making it practically impossible to apply to a general internal combustion engine.
Therefore, it is an object of the invention to eliminate the above drawbacks, and providing a tappet structure which is capable of achieving friction-resistant property and light-weightness with minimum cost.